Metabolic Pathways
A metabolic pathway is a succession of biochemical reactions occurring within a cell. The pathways are controlled by enzymes, which catalyze the individual steps. Metabolic pathways are essential for life; they allow the cell to extract energy from food and to biosynthesize the molecules it needs. The most common type of metabolic pathways include glycolysis, glycogenesis, fatty acid synthesis, the Krebs cycle, the electron transport chain, and the pentose phosphate pathway. (3)
Glycolysis
Glycolysis is the process that produces energy in the body by breaking down glucose. Glucose is a sugar molecule that is found in food and is also produced by the body. The process of glycolysis occurs in all cells of the body and is necessary for life. The first step in glycolysis is the conversion of glucose to two molecules of pyruvate. This step is catalyzed by the enzyme glycolase. The next step is the conversion of pyruvate to acetyl CoA. This step is catalyzed by the enzyme pyruvate dehydrogenase. The final step in glycolysis is the conversion of acetyl CoA to CO2 and H2O. This step is catalyzed by the enzyme acetyl CoA carboxylase.
Glycogenesis
Glycogenesis is the process of making glycogen, a type of complex carbohydrate. Glucose is converted into glycogen by the addition of water molecules. The process is regulated by the hormone insulin, which is released by the pancreas in response to elevated levels of blood glucose. Insulin causes cells to take up glucose from the blood and convert it into glycogen.
Fatty acid synthesis
Fatty acids are the fats essential for human health, and are necessary for the proper functioning of the body. Fatty acids can be synthesized by the body, but there are also some fatty acids that must be obtained from food. The process of synthesizing fatty acids is called fatty acid synthesis.
There are two major types of fatty acids that the body can synthesize: saturated fatty acids and unsaturated fatty acids. Saturated fatty acids have no double bonds, while unsaturated fatty acids have one or more double bonds. The process of synthesizing saturated fatty acids is simpler than the process of synthesizing unsaturated fatty acids.
The Krebs cycle
The Krebs cycle is a process that produces energy in cells. The cycle is named after the scientist who discovered it, Hans Adolf Krebs. It begins with the breakdown of glucose, which releases energy. This energy is used to create a molecule called acetyl coenzyme A (acetyl CoA). The acetyl CoA then enters the Krebs cycle, where it is broken down into carbon dioxide and water. This process releases more energy, which is used to create new molecules of acetyl CoA. The Krebs cycle completes four times for every molecule of glucose that is broken down. The final product of the cycle is water and carbon dioxide.
The electron transport chain
It is a series of proteins found in the inner membrane of the mitochondria. These proteins are responsible for transferring electrons from organic molecules to oxygen, which results in the generation of adenosine triphosphate (ATP), the primary energy source for cells. This chain is composed of four complexes, each of which contains multiple proteins. The first complex, known as complex I, transfers electrons from NADH to ubiquinone. Complex II, also known as succinate dehydrogenase, transfers electrons from succinate to fumarate. Complex III, also known as cytochrome c reductase, transfers electrons from cytochrome c to oxygen. Finally, complex IV (or cytochrome c oxidase) converts oxygen to water.
Pentose phosphate pathway
The pentose phosphate pathway is a metabolic pathway that produces glucose-5-phosphate and NADPH from glucose. It is a series of biochemical reactions that convert glucose-6-phosphate to 5-carbon sugars. The pathway is used to produce energy and to biosynthesize new molecules. This pathway is also called the HMS (hexose monophosphate shunt) and it is also responsible for the production of NADPH, which is used in cellular redox reactions. This pathway occurs in the cytoplasm of cells and is essential for the proper function of the cell.